selftests/bpf: Use reno instead of dctcp

Andrey pointed out that we can use reno instead of dctcp for CC
tests and drop CONFIG_TCP_CONG_DCTCP=y requirement.

Fixes: beecf11b ("bpf: Bpf_{g,s}etsockopt for struct bpf_sock_addr")
Suggested-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200501224320.28441-1-sdf@google.com

tools/testing/selftests/bpf/config

@@ -37,4 +37,3 @@ CONFIG_IPV6_SIT=m
 CONFIG_BPF_JIT=y
 CONFIG_BPF_LSM=y
 CONFIG_SECURITY=y
-CONFIG_TCP_CONG_DCTCP=y

tools/testing/selftests/bpf/progs/connect4_prog.c

@@ -59,12 +59,12 @@ static __inline int verify_cc(struct bpf_sock_addr *ctx,
 
 static __inline int set_cc(struct bpf_sock_addr *ctx)
 {
-	char dctcp[TCP_CA_NAME_MAX] = "dctcp";
+	char reno[TCP_CA_NAME_MAX] = "reno";
 	char cubic[TCP_CA_NAME_MAX] = "cubic";
 
-	if (bpf_setsockopt(ctx, SOL_TCP, TCP_CONGESTION, &dctcp, sizeof(dctcp)))
+	if (bpf_setsockopt(ctx, SOL_TCP, TCP_CONGESTION, &reno, sizeof(reno)))
 		return 1;
-	if (verify_cc(ctx, dctcp))
+	if (verify_cc(ctx, reno))
 		return 1;
 
 	if (bpf_setsockopt(ctx, SOL_TCP, TCP_CONGESTION, &cubic, sizeof(cubic)))